Patent application title: CIRCUIT MODULE

Abstract:

To improve reliability of a circuit module by improving heat release
performance and minimizing thermal influence on a device to be mounted, a
base substrate having a first substrate mounted thereon is fitted into a
lower portion of casing member, and a second substrate is installed in
the upper portion of the casing member so that a spaced area can be
provided. In addition, a drive device to be installed on the second
substrate is positioned off the center of the second substrate.

Claims:

1. A circuit module comprising:a first module substrate including a first
substrate of metal, at least a top surface of the first substrate being
electrically insulated, a plurality of first conductive patterns made of
electrically-conductive material provided on the top surface of the first
substrate, and a power semiconductor device electrically connected with
the first conductive patterns and mounted on the first substrate;a second
module substrate including a resin substrate, a plurality of second
conductive patterns made of electrically-conductive material provided on
a top surface of the resin substrate, and a drive device electrically
connected with the second conductive patterns and controlling the power
semiconductor device; anda casing member of resin holding opposed sides
of the first module substrate and opposed sides of the second module
substrate that is located above the first module substrate with a space
in between, whereinthe drive device is positioned off the center of the
resin substrate.

2. A circuit module comprising:a first module substrate including a base
substrate of metal, at least a top surface of the base substrate being
electrically insulated, a first substrate fixed on the base substrate
with electric insulation, at least a top surface of the first substrate
being electrically insulated, a plurality of first conductive patterns
made of electrically-conductive material provided on the top surface of
the first substrate, and a power semiconductor device electrically
connected with the first conductive patterns and mounted on the first
substrate;a second module substrate including a second substrate of
resin, a plurality of second conductive patterns made of
electrically-conductive material provided on a top surface of the second
substrate, and a drive device electrically connected with the second
conductive patterns and controlling the power semiconductor device; anda
casing member of resin holding opposed sides of the first module
substrate and opposed sides of the second module substrate that is
located above the first module substrate with a space in between,
whereinthe drive device is positioned off the center of the second
substrate.

3. The circuit module according to claim 2, wherein:the first substrate is
a metal substrate mainly comprising Al or Cu and the second substrate is
a glass epoxy substrate.

4. A circuit module comprising:a first module substrate including a Al
base substrate with a rectangular shape, at least a top surface of the Al
base substrate being electrically insulated, a first substrate of Al with
a rectangular shape fixed onto the Al base substrate by an insulating
adhesive and located inside a periphery of the base substrate, at least a
top surface of the first substrate being electrically insulated, a
plurality of first conductive patterns made of electrically-conductive
material provided on the top surface of the first substrate, and a
switching semiconductor device for an inverter, the switching
semiconductor device electrically connected with the first conductive
patterns and mounted on the first module substrate;a second module
substrate including a second substrate of resin, a plurality of second
conductive patterns made of electrically-conductive material provided on
a top surface of the second substrate, and a microcomputer electrically
connected with the second conductive patterns and controlling the
switching semiconductor device; anda casing member of resin being shaped
like a quadrangular prism having a hollow penetrating from an upper
surface to a lower surface thereof with an opening portion, on the lower
surface, abutting four sides of the base substrate, the casing member
having a holding unit for holding a back surface of the second substrate
inserted from an opening portion on the upper surface and located above
the first module substrate with a space in between, whereinthe
microcomputer is positioned off the center of the second substrate.

5. The circuit module according to claim 4 wherein inner walls of the
casing member corresponding to the opening portion on the upper surface
of the casing member have a first side wall abutting the back surface or
a side surface of the second substrate and a second side wall spaced from
the side surface of the second substrate so as to provide spaced area
serving as a ventilation hole.

6. The circuit module according to claim 5 wherein heat generated by the
switching semiconductor device being driven is released outside through
the ventilation hole.

Description:

[0001]This application claims priority from Japanese Patent Application
Number JP2007-252203 filed on Sep. 27, 2007, the content of which is
incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to a circuit module that handles a
large amount of electric power.

[0004]2. Description of the Related Art

[0005]In recent years, environmental disruption, sign of global warming,
and causes of the warming have been reported in newspapers. There exist a
number of the causes, one of which is increased electric power
consumption. The electricity largely depends on petroleum resources now
being depleted, and a problem is emission of carbon dioxide gas into the
atmosphere resulting from combustion of the petroleum. In addition, most
of automobiles are gasoline-powered, which also worsen the problem.

[0006]Understandably, the former, electricity, is essential to drive
electronic devices in every part of the world. Electricity serves as a
power source for a washing machine, an air conditioner, portable devices,
and the like, and is indispensable for all the people of the earth to
maintain cultural life. Thus, the problem is a challenging theme to
solve.

[0007]On the other hand, automobiles have become highly functional. For
example, holding a TV conference within a vehicle or guiding to a
destination by a car navigation system has become possible, a car
air-conditioner is used for cooling, or head lights illuminate bright and
sharply. As the functions become increasingly sophisticated, world's
consumers prefer to buy these automobiles. In other words, unlike the old
days, driving a car while using various functions in the car results in
increased energy consumption. This also holds true for computers or
portable phones.

[0008]In order to achieve these functions, semiconductor devices, such as
so-called power devices, IC, and LSI have been introduced. These devices
are mounted on a mounting board such as a printed circuit board, for
example, and installed in a set of electronic devices. Given this matter,
reduction in power consumption of semiconductor devices, has become an
important issue.

[0009]The electronic devices, especially semiconductor devices, generate
heat when operating, which increases the temperatures of their active
areas, resulting in reduced driving ability. An attempt to enhance the
driving ability leads to further increase in energy consumption.

[0010]In fact, it is necessary to reduce electric power that is consumed
by semiconductor devices themselves by releasing heat of semiconductor
devices to the outside in some way. The trend is clearly seen, for
example, in power MOS devices that are capable of power driving, and
requires some measure to release heat. For this reason, recently, devices
such as inverter modules used in, for example, washing machines,
refrigerators, and drive modules used in, for example, a plasma display
have often been mounted on metal substrates to release heat.

[0011]The metal substrate has its surface covered by an insulating resin,
and the like, and conductive patterns formed thereon. A device necessary
for an inverter circuit, for example, is electrically connected to and
mounted on the conductive patterns.

[0012]However, the number of circuit devices or conductive patterns that
can be built on the top surface of one metal substrate is limited, and it
was thus difficult to integrate on the top surface of one metal substrate
a large hybrid integrated circuit formed of power devices and control
devices. Then, forming conductive patterns in multiple layers on the top
surface of a metal substrate would enable integration of a more
complicated electric circuit. To make conductive patterns in multiple
layers, however, an interlayer insulation layer should be provided
between a lower layer conductive pattern and an upper layer conductive
pattern, which may lead to a problem that the interlayer insulation film
made of resin blocks conduction of heat released from circuit devices to
the metal substrate.

[0013]In addition, if a metal substrate and a printed circuit board are
superposed and arranged within casing member and connected with each
other, a relatively large scale hybrid integrated circuit is achieved
while utilizing an excellent heat release characteristic of the metal
substrate. However, a circuit device made of a semiconductor material
such as silicon, a metal substrate, and a printed circuit board have
different thermal expansion coefficients, which thus results in problems
that a solder connection between a circuit device and a printed circuit
board may have cracks or conductive patterns formed on a metal substrate
or a printed circuit board are disconnected.

SUMMARY OF INVENTION

[0014]The present invention has been made in light of the problems
described above. Firstly, the present invention provides, for solving the
problems, a circuit module having: a first module substrate including a
first substrate of metal, at least a top surface of the first substrate
being electrically insulated, a plurality of first conductive patterns
made of electrically-conductive material provided on the top surface of
the first substrate, and a power semiconductor device electrically
connected with the first conductive patterns and mounted on the first
substrate; a second module substrate including a resin substrate, a
plurality of second conductive patterns made of electrically-conductive
material provided on a top surface of the resin substrate, and a drive
device electrically connected with the second conductive patterns and
controlling the power semiconductor device; and a casing member of resin
holding opposed sides of the first module substrate and opposed sides of
the second module substrate that is located above the first module
substrate with a space in between. In the circuit module, the drive
device is positioned off the center of the resin substrate.

[0015]Secondly, the present invention provides, for solving the problems,
a circuit module having: a first module substrate including a base
substrate of metal, at least a top surface of the base substrate being
electrically insulated, a first substrate fixed on the base substrate
with electric insulation, at least a top surface of the first substrate
being electrically insulated, a plurality of first conductive patterns
made of electrically-conductive material provided on the top surface of
the first substrate, and a power semiconductor device electrically
connected with the first conductive patterns and mounted on the first
substrate; a second module substrate including a second substrate of
resin, a plurality of second conductive patterns made of
electrically-conductive material provided on a top surface of the second
substrate, and a drive device electrically connected with the second
conductive patterns and controlling the power semiconductor device; and a
casing member of resin holding opposed sides of the first module
substrate and opposed sides of the second module substrate that is
located above the first module substrate with a space in between. In the
circuit module, the drive device is positioned off the center of the
second substrate.

[0016]Thirdly, the present invention provides, for solving the problems, a
circuit module comprising: a first module substrate including a Al base
substrate with a rectangular shape, at least a top surface of the Al base
substrate being electrically insulated, a first substrate of Al with a
rectangular shape fixed onto the Al base substrate by an insulating
adhesive and located inside a periphery of the base substrate, at least a
top surface of the first substrate being electrically insulated, a
plurality of first conductive patterns made of electrically-conductive
material provided on the top surface of the first substrate, and a
switching semiconductor device for an inverter, the switching
semiconductor device electrically connected with the first conductive
patterns and mounted on the first module substrate; a second module
substrate including a second substrate of resin, a plurality of second
conductive patterns made of electrically-conductive material provided on
a top surface of the second substrate, and a microcomputer electrically
connected with the second conductive patterns and controlling the
switching semiconductor device; and a casing member of resin being shaped
like a quadrangular prism having a hollow penetrating from an upper
surface to a lower surface thereof with an opening portion, on the lower
surface, abutting four sides of the base substrate, the casing member
having a holding unit for holding a back surface of the second substrate
inserted from an opening portion on the upper surface and located above
the first module substrate with a space in between. In the circuit module
the microcomputer is positioned off the center of the second substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIGS. 1A and 1B are views showing a circuit module according to a
preferred embodiment of the invention.

[0018]FIG. 2 is a perspective view showing the circuit module of FIG. 1.

[0019]FIG. 3 is a view illustrating deformation due to expansion in the
circuit module according to the preferred embodiment of the invention.

[0021]FIG. 5 is a view illustrating notches provided in the circuit module
according to the preferred embodiment of the invention.

[0022]FIG. 6 is view illustrating notches provided in the circuit module
according to the preferred embodiment of the invention.

DESCRIPTION OF THE INVENTION

[0023]With reference to FIG. 1, a configuration of a circuit module
according to an embodiment of the invention will be described
hereinafter. The circuit module mainly comprises a casing member 3 shaped
like a picture frame, a base substrate 1B and a first substrate 1A that
close an opening portion in the lower side of the casing member 3, and a
second substrate 2 that closes an opening portion in the upper side of
the casing member 3.

[0024]The metal substrate 1B is the base substrate and is formed to have a
whole circumference larger than that of the first substrate 1A thereon on
each side by a distance L2. The distance L2 is referred to as an
extension distance that improves withstand voltage property of the first
substrate 1A and a back side of the base substrate 1B in an actually
configured circuit module.

[0025]The casing member 3 is now described. The casing member 3 is shaped
like a quadrangular prism whose interior has been removed. In other
words, it is integrally formed of four side walls, namely, a side wall 3A
on the near side of the drawing, a side wall 3B on the far side, a wall
3D on the right, and a side wall 3C on the left. Thus, the casing member
3 has upper and lower opening portions 20, 21. On the inner side of the
casing member 3 is a convex portion 22 facing inside. Thus, at a position
somewhat lower than the upper opening portion are formed abutting areas
23 supporting the back side periphery of the second substrate 2. As seen
in FIG. 1B, the abutting area 23 is formed on each of the inner walls of
the casing member side walls 3C, 3D and abuts the back side adjacent to
one of the right and left sides of the second substrate 2. On the other
hand, to secure screwing holes 24, 24, the inner walls of the side walls
3A, 3B have areas 25 abutting the second substrate 2 and areas 26 spaced
from the second substrate 2. The heat generated in a space between the
second substrate 2 and the first substrate 1A is released outside through
the spaced area 26.

[0026]In the following, the base substrate 1B and the first substrate 1A
will be described. Each of the two substrates may be formed of an
electrically-conductive material mainly containing Cu, Al, or Fe, for
example, or formed of an alloy. In addition, the substrate may be formed
of a material having good thermal conductivity. The substrate may be
formed of an insulating material such as aluminum nitride, boron nitride,
or the like. Generally, Cu or Al is adopted in terms of cost, and the
description herein is given on the substrates that have adopted Al.

[0027]Since the two substrates are electrically conductive, they should be
electrically insulated. Both surfaces of each of the base substrate 1B
and the first substrate 1A are coated by an anodized film to prevent
scratching. However, since the substrates are to be cut, Al is exposed at
the center of their lateral sides. On the base substrate 1B is fixed the
first substrate 1A by an insulating adhesive. The first substrate 1A is
smaller in size, so that every side of the first substrate 1A is located
inwardly from the corresponding sides of the base substrate 1B by the
distance L2. Furthermore, to the anodized film formed on the top face of
the first substrate 1A is applied an insulating coating 26 onto which a
first conducive pattern 7 formed of Cu is bonded. The conductive pattern
7 includes an island, wiring, an electrode pad, an electrode for a
passive device, and the like. For example, a power semiconductor device 4
includes a BIP type power Tr, a MOS type power Tr, IGBT, and the like,
and electrically connected and affixed to an island. A surface electrode
and the electrode pad of the device are connected by thin metal wire. In
addition, a diode, a chip resistor, a chip capacitor, and the like are
mounted. Furthermore, on the side of the first substrate 1A is provided a
pad for affixing leads to which external leads 29 are affixed by brazing
filler metal. The external leads 29 are long enough to protrude from the
head of the casing member 3 and, as shown in FIG. 4, inserted into
through holes on the mounting substrate prepared separately to be
electrically connected.

[0028]A first module substrate formed by bonding the base substrate 1B and
the first substrate 1A is fitted into the opening portion 20 on the lower
side of the casing member 3. As described previously, the casing member 3
has the convex portion 22. In other words, an L-shaped step is provided
in all the inner side walls. The first module substrate is fixed to the
case member, such that the side surface of the base substrate 1B and the
top surface forming an angle with the side surface are in contact with
the L-shaped steps. Thus, the casing member 3 and the fitted first module
substrate entirely shield the circuit module except the opening portion
21.

[0029]In the following, the second substrate 2 will be described. The
second substrate 2 is made of a resinous substrate and a preferable
example is a glass epoxy substrate called a printed circuit board. The
second substrate 2 has conductive patterns with more than one layer
formed at least on the top surface. Generally, the conductive patterns
may be selected from one layer on the top surface, two layers on each
surface, four layers on each surface and the like. To be specific,
density of a device to be incorporated determines how many layers the
second conductive pattern 30 will have. As similar to the first
conductive pattern 7, the second conductive pattern 30 includes an
island, wiring, an electrode pad, an electrode for a passive device, and
the like. Then, a device to be mounted on the second conductive pattern
30 is an active device or a passive device, that is, a device 31
characteristic of the preferred embodiment of the invention.

[0030]The drive device 31 is an IC for driving and controlling the power
semiconductor device 4 and includes a microcomputer, for example. The
drive device 31 also includes a Tr, a diode, a chip resistor and a chip
capacitor.

[0031]In addition, near the right and left sides of the second substrate 2
are through holes 32 into which the external leads 29 are inserted. The
through holes 32 electrically connect the circuit formed on the first
substrate 1A with the circuit formed on the second substrate 2.

[0032]The second module substrate is provided inside the casing member 3
through the upper opening portion 21. As described previously, the
abutting areas 23, 25 are provided on the inner walls, of the casing
member 3, on which the second substrate is installed.

[0033]To prevent the brazing filler metal from cracking and external
atmosphere from entering the interior through the spaced-apart areas 26,
resin completely sealing devices of the first substrate is provided by
potting, or the like as shown in FIG. 1A, before the second substrate is
provided. Then, a distance from the top surface of the first substrate 1A
to the back side of the second substrate 2 is set to L1. The thickness of
the coating resin is S1, and a space S2 is provided. Air in the space S2
is heated by the first module substrate, and released outside through the
spaced-apart areas 26. Thus, to cause air circulation, at least two
spaced-apart areas are formed. In this embodiment, actually, four
spaced-apart areas 26 are formed.

[0034]In addition, a resin for completely sealing devices is provided
above the second substrate 2, as necessary. Now, the drive device 31 is
mounted in bare state in FIG. 1A, and a resin-sealed semiconductor device
is formed in FIG. 1B. Although they do not agree, in fact, either of them
is acceptable.

[0035]FIG. 2 is a perspective view of the circuit module, which is shown
separately in order to clarify a relation of the casing member 3 and the
second substrate 2.

[0036]FIG. 3 illustrates thermal relationship of the resinous casing
member 3, the first module substrate 40, the second module substrate 41,
and even the external leads 29. By way of example, the circuit module
provides an inverter circuit of the air conditioner and is mounted to an
outdoor unit 50 as shown in FIG. 4, for example. FIG. 4 is a cutaway view
of the outdoor unit 50 where 51 denotes an air circulating fan behind
which a heat exchanger is located. To the right of the fan 51 is
installed a frame 52 of Al or Fe. A compressor 53 is installed under an
inner divider plate 52A, and a printed circuit board with circuit
components mounted thereon is fixed above the inner divider plate 52A. In
fact, the figure was simplified because there are quite complicated
circuit components. In addition, adjacent to the left of the inner
divider plate 52A is a printed circuit board that is perpendicular to the
inner divider plate 52A and that extends vertically. The circuit module
54 according to the preferred embodiment of the invention is mounted on
the printed circuit board. A radiating fin 55 is attached to the back
surface of the base substrate 1B that constitutes the back surface of the
circuit module. The compressor 53, a fan motor, and the circuit
components emit heat in the outdoor unit, and the main body of the
outdoor unit is installed outdoors. Thus, temperatures inside the outdoor
unit rise. Consequently, the circuit module 54 itself is subjected to
high temperature.

[0037]Now, the expansion coefficient of Al is 23×10-6/°
C. (that of Cu is 20×10-6/° C.). By way of example, a
resin substrate has al of 11 to 12×10-6/° C. in the x-y
direction, and 25 to 30×106/° C. in the z direction. In
addition, a of Si is 2.0 to 4.0×10-6/° C. Those
coefficients significantly differ from each other. In fact, when
temperature of the outdoor unit goes high, the lower part of the casing
member 3 considerably expands because of a of the two Al substrates,
whereas the printed circuit board side does not expand much. Then, when
the casing member 3 itself expands, it will transform into a trapezoidal
shape. Accordingly, the printed circuit board 41 warps so as to be convex
downward. The curvature means that the printed circuit board warps most
at the intersecting point of the center lines in FIG. 1B.

[0038]Thus, the second substrate 2 needs to arrange the circuit device off
the center area of the second module substrate 41 in FIG. 3. In other
words, the arrangement of the circuit device off the center area enable
reliability of electrical connection of brazing filler metal, metal wire,
and the like to be improved.

[0039]Since a greater number of terminals are provided especially in a
microcomputer 31 that is a drive device than in other semiconductor
devices, reliability can be improved by moving the drive device 31 off
the center.

[0040]In the following, a further heat release route is described with
reference to FIG. 2, and FIG. 4 to FIG. 6. The reference numeral 60 in
FIG. 4 shows air flow routes A to B of the air flow to be generated when
air rises by heating or effect of the fan 51. Naturally, channels of the
radiating fin 55 are provided vertically. Thus, if notches along the air
flow routes A to B are also provided in the circuit module 54, the heat
release performance will be further improved.

[0041]In FIG. 2, the notches are designated by the reference numerals 70
to 73, and also shown in FIG. 5 and FIG. 6. The near side of the circuit
module of FIG. 5 faces the printed circuit board 74 in FIG. 4. FIG. 6 is
a schematic view of the circuit 54 shown in FIG. 4 and viewed from the
top. Encircled black point symbols as shown in the notches 70, 71 or the
channels indicate the air flow routes A to B in FIG. 4. The direction of
the air flow is from the back to the front of the page.

[0042]In summary, heat from the base substrate accumulates in the space
under the second substrate 2 in FIG. 1A and flows into the space
surrounded by the casing member 3 and the sealing resin of the second
substrate through the spaced-apart areas 26 in FIG. 1B. Then, flow in the
air flow routes A to B in FIG. 4, namely, the air flow routes for flowing
air upward through this space are generated. Hence, highly efficient heat
release can be achieved.

[0043]As shown in FIG. 3, in the preferred embodiment of the invention, it
is possible to space a printed circuit board from a metal substrate
through use of casing member. However, deformation of the casing member
due to thermal expansion of the metal substrate or deformation of the
printed circuit board due to overheating of the printed circuit board by
a power semiconductor device can by no means be eliminated. Thus, it is
possible to shunt electrical connection to the most curved area by
offsetting a circuit device from an intersecting point of the center
lines as shown in FIG. 1B. In particular, as IC and LSI that drive a
power semiconductor device are most important components of an inverter,
etc., improved reliability can be achieved.